Overview

Brief Summary

Biology

Compared with most of its Galapagos relatives, the Cocos finch is more of a generalist in its foraging habits. However, individual birds tend to specialise in a small selection of the various techniques employed by the species as a whole. For instance, while some Cocos finches may forage mainly for insects resting on foliage, others may feed predominately on soft fruit or nectar (2) (6) (7). The comparatively wide range of foraging habits exhibited by the Cocos finch is thought to be indicative of the absence of competition (6). Little is known about the reproductive biology of the Cocos finch, but the clutch size appears to be two eggs and nesting occurs year round with a peak between January and May (2) (8).

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Description

Darwin's finches are a group of fourteen closely related birds, celebrated as an example of how natural selection can lead to the evolution of different species from a single lineage (3). While thirteen of Darwin's finches are found on the Galapagos, the fourteenth member is confined to the small island of Cocos, just over 600 kilometres to the northeast (2) (3) (4). Like the ground finches of the Galapagos, the adult male plumage of the Cocos finch is completely black (2) (5), while the female Cocos finch is blackish-brown above with olive-brown streaks, and paler buff below with black streaks (2). Darwin's finches are characterised by a wide spectrum of beak forms, with the slender, pointed beak of the Cocos finch being particularly distinct (2) (5) (6).

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Ecology

Habitat

Habitat and Ecology

It occupies every available habitat on the island, including Hibiscus thickets along coasts, woodland, open country and closed-canopy forest (Smith and Sweatman 1976, Sherry 1985, Stiles and Skutch 1989), and is common in disturbed vegetation (Slud 1967). It is a generalist (Smith and Sweatman 1976), but individual birds usually specialise in one or a few of the various foraging techniques employed by the species as a whole (Stiles and Skutch 1989). Nesting occurs throughout the year, but is mostly concentrated in January-May (Stiles and Skutch 1989).

IUCN Red List Assessment

Although its high tolerance of degraded habitats suggests that this species is unaffected by the impact of introduced herbivores on forested areas, it is listed as Vulnerable because it has a very small range and is thus susceptible to chance catastrophes.

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Threats

Rats and cats are potential predators, and grazing by feral deer, pigs and goats degrades natural habitats on the island. There is also low-level disturbance from increasing tourism. However, none of these appears to have adverse affects.

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Although rats and cats are potential predators, and feral pigs, goats, and deer are known to reduce habitat quality, the Cocos finch appears to be fairly tolerant of disturbance and remains relatively abundant. However, because it is confined to such a small area, there are concerns that a single catastrophic event could eliminate the entire Cocos finch population (2).

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Conservation

Although there are no conservation measures presently underway for the Cocos finch, there are future proposals to assess the role of various factors on the species' abundance (2). Furthermore, the whole of Cocos Island is designated a National Park and a UNESCO World Heritage Site (2) (4). As a World Heritage Site, Cocos Island is subject to a management plan that aims to ensure the island's conservation through the protection of sensitive sites, the elimination of alien species, the promotion of scientific research, and the control of tourism (4).

It is a chunky 12 cm long finch weighing around 12.5 g and with a black decurved pointed bill. The male is entirely black, while the female is a heavily streaked brown, with a paler underside. The young are similar but have yellow bills. The standard clutch is two brown-spotted white eggs, which are hatched in a roughly spherical nest built at the end of a tree branch.

The Cocos finch is the most abundant landbird on Cocos Island. It can be found in every habitat on the island and eats a wide range of plant and insects as food.